Multiphase simulation and parametric study of direct vapor generation for a solar organic Rankine Cycle

Parabolic trough collectors coupled with Organic Rankine Cycles are an attractive option for decentralized power generation. This work is dedicated to the parametric study of a parabolic trough collector system filled with benzene under solar irradiation for use in an Organic Rankine Cycle; the Computational Fluid Dynamics software ANSYS FLUENT was used in the study. Different inlet temperatures (465, 475 and 485 K), mass fluxes (168, 336 and 504 kg/m2s), and solar-concentrated heat fluxes (15.1, 18.5 and 22.2 kW/m2) are used in the simulations. The numerical model is validated with experimental data to a good concordance (maximum measured error for outlet equilibrium vapor quality and temperature is about 6 % and 0.01 %, respectively). The results indicate that (1) the inlet temperature does not have an effect in the fluid boiling behavior, (2) increasing the mass flow rate decreases the fluid evaporation rate, (3) the fluid evaporation rate is directly affected by the solar heat flux and (4) the mass flux affects the point where evaporation begins occurring (tube lengths of 10, 15 and 25 m for mass fluxes of 168, 336 and 504 kg/m2s, to 15.1 kW/m2, respectively.) Results also show that an excessive heat flux can result in large thermal gradients inside the collector (hence, overheating), and an excessive mass flow will delay the net vapor generation point.

Automated summary

Parabolic trough collectors coupled with Organic Rankine Cycles are studied parametrically with benzene under solar irradiation using Computational Fluid Dynamics software. Results show that inlet temperature does not affect fluid boiling behavior, increasing mass flow rate decreases fluid evaporation rate, and fluid evaporation rate is directly affected by solar heat flux and mass flux.